stands for Qualcomm Reference Design . It’s a standardized board that OEMs use to jump-start their own devices. The QRD variant of SDM439 comes with pre-defined peripherals, power management (PM8953/PMI8940), and crucially — a fixed USB configuration used for debugging, flashing, and factory testing.
| Mode | USB VID:PID | Driver needed (Windows) | Purpose | |------|-------------|------------------------|----------| | | 05C6:9091 | Microsoft MTP driver | File transfer | | Fastboot | 18D1:D00D | Google fastboot driver | Flashing boot/recovery | | EDL (Emergency Download) | 05C6:9008 | Qualcomm HS-USB QDLoader 9008 | Brick recovery, flashing full firmware | | Diag (Diagnostic) | 05C6:9025 | Qualcomm HS-USB Diagnostics | QXDM, QPST, modem logging | | ADB | 18D1:4EE8 | Google USB driver | Development debugging |
| Symptom | Probable Cause | Solution | | :--- | :--- | :--- | | | Windows is re-installing a generic modem driver automatically. | Disable automatic driver updates via Group Policy (gpedit.msc) or use pnputil /delete-driver to remove conflicting drivers. | | Error 10: Device cannot start | Incompatible driver version or corrupted INF file. | Uninstall the device, check "Delete driver software," then reinstall using Method 2 above. | | Device shows as "Android ADB Interface" | The device is in fastboot/bootloader mode, not EDL. | Re-enter EDL mode by shorting TEST_POINT on the SDM439-QRD board (specific coordinates vary by model). | | QFIL fails with "Sahara protocol error" | The driver is installed, but the handshake timing is off. | Use a USB 2.0 port (not USB 3.0). Replace the USB cable with a high-quality data sync cable. | | Signature enforcement blocks installation on Windows 11 | Windows 11 requires a more complex disabling method. | Use bcdedit /set testsigning on in an admin command prompt, then restart. (Reboot with bcdedit /set testsigning off after). |